1. Field of the Invention
The present invention relates generally to pressure and temperature measurement devices. The present invention relates more specifically to the use of liquid crystal materials and charge coupled device technologies in combination for the measurement and monitoring of small pressure and temperature variations with a high degree of topographic resolution.
2. Description of the Related Art
A problem well known in the medical field is the need to quickly and accurately ascertain a patient's blood pressure and temperature. This may be required infrequently in conjunction with a physical or routine check-up or may need to be constant as when monitoring patients with prolonged illnesses such as high blood pressure and/or unstable temperatures.
Some blood pressure monitoring devices have been created to provide constant information regarding blood pressure with the least amount of inconvenience to the patient. Such systems typically are worn around the wrist and attempt to apply an array of pressure sensing elements with constant pressure over an artery. These systems principally select one pressure sensing element from the array from which to calculate the blood pressure in the artery. U.S. Pat. Nos. 4,269,193 and 4,802,488, both by Eckerle, describe various methods of optimizing the selection of the single pressure element from which the blood pressure will be measured. In the Eckerle patents information about the patient's physical characteristics is input into the device and used to estimate the diameter of the underlying artery. Then, based on diastolic and systolic pressure and pulse amplitude values, the device selects a pressure-sensing element calculated to be near the center of the artery from which the blood pressure is monitored. A drawback of this device and others like it, is that a single pressure-sensing element is used as the basis for all blood pressure measurements.
Other pressure-sensing devices have been developed which increase the number of individual pressure-sensing elements contacting the area to be measured. U.S. Pat. No. 5,277,067, issued to Holland et al., uses standard integrated circuit fabrication techniques to create an array of pressure sensor elements. The fabrication process includes forming a hole in an insulating layer deposited on an electrical cathode layer, depositing material to form an electrical cathode tip into the hole, and bonding an electrical anode layer onto the insulating layer so as to be slightly separated from the cathode tip. Each pressure sensor element detects changes in pressure due to variations in the initial separation between the anode layer and the cathode tip based on the electric current produced by tunneling or electron field emission.
Other pressure-sensing devices have been constructed which make use of the optical properties of crystal materials to detect variations in pressure. One such device is described in U.S. Pat. No. 5,309,767, issued to Parmar et al. The device described by Parmar consists of a liquid crystal material placed between two transparent, electrically conductive films which are biased by a voltage. The bias voltage creates an electric field that results in an initial state of orientation of the liquid crystal material. Subsequent application of pressure to one of the flexible films results in a change in the electric field and a corresponding change in the orientation of the liquid crystal. The intensity of polarized light directed into the liquid crystal and detected by an analyzer changes as a function of the applied pressure and provide a means of measuring the pressure variations. While the liquid crystal material is grouped into minute pockets within the pressure sensor, the device measures the cumulative change in pressure rather than being able to detect the specific change in pressure experienced by each pocket.
Such prior art pressure-sensing devices, as previously described, suffer from certain inherent problems. Typically, they are unable to detect small variations in pressure at a number of points simultaneously and, therefore, lack high spatial or topographic resolution. In addition, none of the prior art devices combine liquid crystal based pressure or temperature sensors with high resolution charge coupled devices to provide a full solid state array.